1. Field of the Invention
The present invention relates to an image forming apparatus, a process cartridge, and an image forming method.
2. Description of the Related Art
In electrophotographic image forming apparatuses, conventionally, a residual toner attached to the surface of an image bearing member after a toner image is transferred to a recording medium or an intermediate transfer body in an image forming step has been removed by a cleaning unit.
As the cleaning unit, a cleaning blade is used because of its simple configuration and excellent cleaning performance. The cleaning blade is usually composed of an elastic member made of a polyurethane rubber or the like, and a supporting member. The base end of the elastic member is supported by the supporting member, and an abutment part (tip ridge line part) of the elastic member is pressed on the surface of the image bearing member to retain a toner remaining on the surface of the image bearing member, scraping the toner off for removal.
However, as illustrated in FIG. 1A, in a cleaning blade 62 made of a polyurethane rubber, the cleaning blade 62 is pulled in the moving direction of an image bearing member 123 by the increase in friction force between the image bearing member 123 and the cleaning blade 62, and an abutment part (tip ridge line part) 62c of the cleaning blade 62 is thus exfoliated. Furthermore, if cleaning is continued while the abutment part 62c of the cleaning blade 62 being exfoliated, local abrasion X occurs at a position on a tip surface 62a of the cleaning blade 62, away from the abutment part 62c by several μm, as illustrated in FIG. 1B. If cleaning is further continued in such a state, the local abrasion X is increased, eventually resulting in the lack of the abutment part 62c, as illustrated in FIG. 1C. Such lack of the abutment part 62c causes a problem of making it impossible to normally remove toner by cleaning, causing cleaning failure. Herein, numeral 62b denotes a lower surface of the cleaning blade in FIG. 1A to FIG. 1C.
Then, in order to suppress exfoliation of the abutment part (tip ridge line part) of the cleaning blade, which abuts the surface of the image bearing member, it is attempted to increase the hardness of the abutment part, thereby hardly deforming the abutment part. For example, it has been proposed to provide a surface layer including an ultraviolet curable resin on an abutment part of a cleaning blade or an elastic member to increase the hardness of the abutment part, thereby preventing the abutment part from exfoliating and deforming (see Japanese Patent No. 3602898, Japanese Patent Application Laid-Open No. 2004-233818, and Japanese Patent Application Laid-Open No. 2010-152295).
However, the ultraviolet curable resin for use in such a proposal has a high crosslink density, and therefore, there is a problem that when the surface layer is provided on the abutment part, the cure shrinkage upon curing is high to cause cracking of the surface layer and peeling of the surface layer.
There is also a problem that if the durability of the cleaning blade is low, the pressing force of a charging roller cannot be increased to make unstable the contact state of the charging roller and an image bearing member, and a uniform charge potential is not achieved.
Accordingly, there is demanded for providing an image forming apparatus in which a cleaning blade capable of maintaining good cleanability over a long period is used to thereby make it possible to increase the pressing force of a charging roller, and the charge potential is stabilized without contamination of the charging roller to generate no linear abnormal image.